This invention relates to a method of sterilizing a diffusion-restricted area in a chamber by condensing a vapor sterilant in the chamber, and revaporizing the condensed vapor sterilant.
Medical instruments have traditionally been sterilized either by heat, especially steam, or with a chemical, such as formaldehyde or ethylene oxide. There are drawbacks to both of these sterilization methods.
Many medical devices are sensitive to heat, moisture, or both. Formaldehyde and ethylene oxide are both toxic gases that pose potential hazards to healthcare workers.
Sterilization with liquid hydrogen peroxide has been found to require high concentrations of sterilant, long exposure times and/or high temperatures. Sterilization with hydrogen peroxide vapor rather than liquid hydrogen peroxide has advantages over other chemical sterilization approaches (see, for example, U.S. Pat. Nos. 4,169,123 and 4,169,124). The combination of hydrogen peroxide with a plasma provides certain additional advantages, as disclosed in U.S. Pat. No. 4,643,876, issued to Jacobs et al.
While sterilization with hydrogen peroxide vapor in combination with a plasma has been found to be effective in sterilizing xe2x80x9copenxe2x80x9d systems, it is not effective in sterilizing articles having diffusion-restricted areas, because the method is dependent on diffusing the vapor sterilant into close proximity with the article to achieve sterilization. Articles having diffusion-restricted areas such as the interior of lumens, are sterilized only with high concentrations of sterilant, extended exposure times and/or elevated temperatures. Sterilization of long, narrow lumens therefore is a challenge.
Sterilization methods that use hydrogen peroxide vapor generated from an aqueous solution of hydrogen peroxide have certain disadvantages because:
1. Water has a higher vapor pressure than hydrogen peroxide and will vaporize faster than hydrogen peroxide from an aqueous solution.
2. Water has a lower molecular weight than hydrogen peroxide and will diffuse faster than hydrogen peroxide in the vapor state.
Because of these factors, when an aqueous solution of hydrogen peroxide is vaporized in the area surrounding the items to be sterilized, the water reaches the items first and in higher concentration. The water vapor therefore becomes a barrier to the penetration of hydrogen peroxide vapor into diffusion restricted areas, such as small crevices and long, narrow lumens. One cannot solve the problem by using more concentrated hydrogen peroxide, because concentrated solutions of hydrogen peroxide at concentrations greater than 65% can be hazardous, because of the strong oxidizing nature.
Cummings et al. (U.S. Pat. No. 4,952,370) discloses a sterilization process where aqueous hydrogen peroxide vapor is first condensed on the article to be sterilized, and then a source of vacuum is applied to the sterilization chamber to remove the water and hydrogen peroxide from the article. The liquid peroxide on the article is effective at sterilizing the surface, but it is ineffective at sterilizing diffusion-restricted areas, such as the interior of lumens, because the method still depends on the diffusion of hydrogen peroxide vapor into the lumen to effect sterilization.
Jacobs et al. (U.S. Pat. No. 4,943,414) discloses a process in which a vessel containing a small amount of vaporizable liquid sterilant solution is attached to a lumen, and the sterilant vaporizes and flows directly into the lumen as the pressure is reduced during the sterilization cycle. This system has the advantage that the water and hydrogen peroxide vapor are pulled through the lumen by the vacuum, increasing the sterilization rate for lumens, but it has the disadvantage that a vessel must be attached to each lumen to be sterilized. Potentially, the area between the vessel and the lumen may be occluded from the sterilization process. In addition, water vaporizes more rapidly than the hydrogen peroxide, and it precedes the hydrogen peroxide vapor into the lumen.
Childers et al. (U.S. Pat. No. 5,492,672) disclose a process for sterilizing narrow lumens. The process uses a multicomponent vapor sterilant and requires successive alternating periods of flow of vapor sterilant and discontinuance of the flow. A complex apparatus is used to accomplish the method. Because flow through of vapor is used, closed end lumens are not readily sterilized by the method.
There is a need for a simple and effective method of sterilizing the interior of long, narrow lumens.
One aspect of the present invention relates to a method for enhancing the sterilization of a lumen device in a chamber. The method comprises introducing sterilant into the chamber from a source of sterilant, condensing the vapor sterilant in the chamber, reducing the pressure in the chamber below the vapor pressure of the vapor sterilant to revaporize the condensed vapor, and maintaining the device in chamber until it is sterilized.
Preferably, the sterilant comprises hydrogen peroxide. Advantageously, the sterilant has a vapor pressure less than the vapor pressure of water. The source of sterilant preferably comprises hydrogen peroxide. The source of sterilant can be a liquid, aqueous solution, or a solid. Advantageously, the source of sterilant is in an enclosure in fluid communication with the chamber. Preferably, the source of sterilant in the enclosure is a liquid, and the liquid is vaporized into the chamber. The source of sterilant can also be located in the chamber.
Advantageously, the source of sterilant is concentrated while it is introduced into the chamber. In some embodiments, the source of sterilant is a solid peroxide complex. Preferably, the vapor sterilant is condensed inside the lumen.
Condensing the vapor can comprise increasing the pressure in the chamber to above the vapor pressure of the vapor sterilant, venting the chamber to atmospheric pressure, introducing more sterilant into the chamber, or reducing the pressure in the chamber below the vapor pressure of the vapor sterilant and then increasing the pressure in the chamber to condense the vapor sterilant.
Advantageously, the pressure in the chamber is controlled by opening or closing a valve between the chamber and a vacuum pump. One or more steps of the method can be repeated one or more times in any order.
Preferably, at least a portion of the condensed vapor is inside the lumen, and the condensed vapor inside the lumen is revaporized. Advantageously, revaporizing the condensed vapor in the chamber also concentrates the vapor sterilant.
Maintaining the device in the chamber can comprise maintaining the chamber at constant pressure, varying the pressure in the chamber, reducing the pressure in the chamber, or increasing the pressure in the chamber. Advantageously, the device is also exposed to plasma. Preferably, the exterior of the device is sterilized prior to reducing the pressure in the chamber and revaporizing the condensed vapor. In some embodiments, the revaporizing is repeated.